The next time you kill a deer, save the skin and some of the insides.

Cut the liver, heart, and kidneys up into pieces.

Out of your dog's sight, drag the skin thru the woods. Put some of the cut up bits on top of the skin.

Take the dog where you started your drag and get him on the trail. Think of a command you want to start the dog tracking and say it over and over as the dog tracks. If he gets off a little and doesn't regain the trail, guide him back to it.

When he gets to the skin, he gets the treat. Give him lots of praise.

Repeat the process a few times, until you are sure he can do it on his own. I made a game of it, and even increased the degree of difficulty as the dog tracked better. Once you have made a game of it, you are good to go.